Although the manner in which two or more tones interact to produce a response in a single auditory nerve fiver has been the subject of several research studies, the phenomenon is still not fully understood. The goal of the research proposed here is to gain a better understanding of some aspects of the neural encoding of complex tones in the primary auditory afferents. We propose to study in a systematic and quantitative manner what has come to be called "two-tone suppression" in the auditory nerve of the cat. The phenomenon under consideration refers to the ability of one tone, the suppressor, to reduce the response to another tone, the excitor. Our primary objectives are as follows: to extend our earlier woek in this area to encompass more stimulus situations, particularly where both tones are excitatory; to investigate suppression effects when a third tone is added and when the suppressor is a bnad of noise; to study the relationship between suppression and the generation of distortion products in the cochlea; and to meld these results into a unified theory of auditory nerve response to complex tones. Hypotheses that are particularly interested in testing are: a. that suppression magnitudeis in part determined by spatial relationships among traveling waves in the cochlea, b. that the mechanism underlying supprassion is related to the mechanism which generates distortion products, c. that suppression effects are primary determinants of interactions observed in neural encoding of complex tones, and d. that the manner in which complex tones are resolved mechanically is independent of the locus of stimulaton in the cochlea. In performing these studies, we will make use of analyses both of the discharge rate elicited by the stimuli and of temporal or phase-locked aspects of the response. Taken together, the data generated here should resolve certain questions regarding the encoding of complex tones in the cochlea and should provide greater insight into the nature of frequency analysis wihtin the cochlea.